Microscopic marine plants (called phytoplankton) contain chlorophyll, a green pigment they use during photosynthesis. Using satellite sensors, we can measure chlorophyll concentrations in oceans, lakes and seas to indicate the distribution and abundance of phytoplankton. Phytoplankton are the base of the marine food chain and, therefore, are a good indicator of the abundance of life in a body of water. (Data from Coastal Zone Color Scanner [CZCS]) Sensor: Nimbus 7/CZCS. Data Start Date: 1/1/84. Data End Date: 6/30/86.